This study is to determine whether administration of testosterone to sedentary, elderly men with relative testosterone deficiency improves muscle composition and performance. Hypotheses to be tested: a) Testosterone administration leads to increases in skeletal muscle mass. b) Testosterone administration leads to improved musle strength and performance. c) Testosterone increases secretion of GH IGF-I, which may contribute to changes in muscle composition. Specific Aim 2: To determine whether the addition of an exercise program will enhance the effect of testosterone administration on muscle mass and performance in sedentary, elderly men with relative testosterone deficiency. Hypothesis to be tested: a) A resistance exercise program augments the benefits of testosterone on skeletal muscle mass. b) A resistance exercise program augments the benefits of testosterone on muscle strength and performance.